Normally such a steering angle sensor device operates on an optical basis and serve for detecting the angular position of a steering wheel at a given moment. After its detection the current angular position is transmitted as serial information to control device connected to the sensor.
The angular position transmitted as serial information respectively the correspondingly transmitted angle value ranging between +/-720 degrees. The transmitted information includes the sign preceding the absolute value, a possible error code, and the initialization state. In most cases the steering wheel cannot be turned through the entire angle range, but only between approximately +/-540 degrees.
Analytically, the transmitted absolute value is composed of two information elements.
a converted angle value from light sensors which give the exact angle within a complete steering wheel revolution from 0 to 360 degrees, whereby the degree of resolution 2.5 degrees; PA1 a counted value which characterizes the revolution segment wherein the steering wheel is moved. There are four revolution segments which cover the detectable range within -720 degrees and +720 degrees, whereby the first revolution segment lies between 0 to 360 degrees, the second revolution segment between 362.5 degrees to 720 degrees, the third revolution segment from -2.5 degrees to -360 degrees and the fourth revolution segment between -362.5 degrees to -720 degrees. However the second and the fourth revolution segment, cannot be fully traversed by the steering wheel. PA1 upon to the occurrence of a coding error, whereby the read-in light barrier signals assume implausible values, which can occur due to mechanical tolerances of the contact spiral, or the coding path to the optical steering wheel sensor device or due to the influence of an electric interference, e.g. from EMV-irradiation; and PA1 due to the occurrence of a voltage drop in the board network of the motor vehicle, wherefrom a RESET-process is triggered in the optical steering angle sensor device.
The angle value is unequivocal due to the use of a code disk. The segment assignment is derived from the counted value. The counted value is always changed when a passage of the steering wheel through zero takes place.
Therefore it is essential for the correct indication of the steering wheel position that the counted value never be lost. Furthermore when the steering angle sensor device is set into operation, it is necessary to perform an initialization of the steering angle sensor by applying the same to the motor vehicle operational voltage, since otherwise the counted value would be set to a preferred value which would not at all correspond to the actual value at the moment.
The steering angle sensor device is initialized by turning the steering wheel from its right stop to the left stop, or from the left stop to the right stop, whereby three passages of the steering wheel through zero are performed therewith. Only after that is the assignment of the revolution segments is clearly established; the status of the initialization is set and the given steering wheel value can be processed as valid by the connected control devices.
The initialization state of the steering wheel angle sensor device can be forcibly reset in various ways during the practical operation of the motor vehicle.
After a cancellation or a forced resetting of the initialization state optical steering angle sensor device, the noninitialized state of the combination consisting of the optical steering angle sensor device and the thereto connected control devices is brought to the attention of the driver, by means of a control light on the dash board. This control light turns off only when the driver of the motor vehicle performs a complete reinitialization, i.e. when the driver of the motor vehicle moves the steering wheel from its left end position to its right end position or vice versa, whereby then the three passages of the steering wheel through the zero position result, which allow a correct assignment of the revolution segments. Such a complete reinitialization of the optical steering angle sensor device is therefore expensive, and at the same time poses the question whether such a procedure should be imposed on the driver.